The present invention relates to an electrically-actuated ignition circuit or system which acts fast in traffic accidents such as crashes or the like to actuate a gas generator for producing a volume of high-pressure gas to be filled in a separate gas bag for inflation so as to safe-guard a driver against sudden impacts or shocks due to the crashes or sudden stops.
When a driver, who is riding in a motor vehicle such as an automobile car at high speeds, happens to encounter a traffic accident such as a crash, he will receive a considerable amount of sudden shock or impact which may place him in an extremely dangerous condition.
There is a safety-equipment device known as a gas bag apparatus which is to be actuated immediately in emergencies to inflate a gas bag designed to safeguard the driver against such sudden shock or impact. The known apparatus is constructed such that it is actuated either when a motor vehicle is shocked by impacts of over a given limit or by means of a radar sensor which predicts a given level of a possible near crash so that a gas bag installed in a driver's seat may be inflated so fast as to hold the driver to his seat. This keeps the driver's body restrained in such emergencies, thereby safeguarding the driver against the impact or shock. It is known that the apparatus acts fast to feed a volume of high-pressure gas to a gas bag for inflation.
There are also known different types of sources for supplying the high-pressure gas. One is a gas bomb or vessel in which is filled a volume of compressed gas. However, this type of gas supply has disadvantages since a bomb or vessel must be large enough to contain a large volume of gas under highly compressed pressure. This is because it is ordinarily difficult or impossible to obtain a desired volume of gas from the bomb as the temperature of the gas is drastically reduced by the action of adiabatic expansion.
There is another supply of high-pressure gas known as a hybrid-type gas generator. This hybrid-type gas generator is so called because it is a combination of high-pressure gas and chemical substances for generating high-temperature gas when burned. The gas generator includes gas producing substances and an electrically-heated filament for burning the substances, and is separately installed in a high-pressure gas filled bomb. When the filament is energized upon a shock or impact, it ignites the substances for burning to produce high-temperature gases. This provides a dual effect since it produces a volume of high-temperature gas and increases the volume of the high-pressure gas in the bomb by adding the high-temperature gas thereto. Therefore, it can finally supply a sufficient volume of high-pressure gas. By using the gas generator, it is possible to construct a gas bomb of a relatively small size.
As explained above, the hybrid-type gas generator includes an electrically-heated filament for burning the gas-producing substances, but actually needs another electrically heated filament for exploding a detonator to break a seal provided in a bomb for supplying the produced gas to a separate gas bag. According to this conventional type bomb, the two filaments act at the same time when a shock or impact is sensed, so that the bomb is made to lead gas to the gas bag just as the gaseous products are generated. This may present no particular problem as long as the gas generator functions properly. However, it has problems with respect to the safety operation when trouble occurs, since there is provided no control function by which operational priorities are given to any one of the two filaments. Practically, it may conceivably happen that the detonator-explosion filament will act intolerably later than the other filament. In such a situation, the bomb would have an explosively increased internal pressure which might possibly lead to either exploding the bomb or breaking the seal in the bomb. In the latter case, the gas bag would be inflated so fast that it might seriously injure the driver.